Signal status diagnosing device for control actuator as driven object

ABSTRACT

A device for diagnosing signal status of a driven object includes an insulation transformer, a signal generating device, a current measuring device, a feedback device, and a voltage measuring device. The insulation transformer has an intermediate tap at a midpoint of its primary winding. The signal generating device generates periodically vibrating voltage and includes a rectangular wave pulse voltage and alternating voltage. The current measuring device is connected to the intermediate tap of the primary winding to measure a current. The feedback device converts the current flowing from the intermediate tap of the primary side to a voltage corresponding to the drive voltage and feeds back the converted voltage to the input drive voltage signal. The voltage measuring device measures the voltage added with the feedback voltage. Diagnosis of the signal state is performed based on measurement results of the current measuring device and voltage measuring device.

RELATED APPLICATIONS

The present application is based on, International Application No.PCT/JP2009/050599, filed Jan. 9, 2009, and claims priority from,Japanese Application Number 2008-005075, filed Jan. 11, 2008, thedisclosure of which is hereby incorporated by reference herein in itsentirety.

TECHNICAL FIELD

The present invention relates to a device for diagnosing signal statusof a control actuator as a driven object, specifically for diagnosingwhether a voltage signal sent to a control actuator which is a drivenobject such as a servo valve which is opened or closed upon receivingthe signal or controlled between full opened and full closed state inaccordance with the signal for the purpose of controlling a plant orequipment, is transmitted to the driven object accurately and whetherthere is a braking of wire or short circuit occurred.

BACKGROUND ART

There have been known a control actuator such as a servo valve which isopened or closed upon receiving a voltage signal or controlled betweenfull opened and full closed state in accordance with the voltage signalused in a plant or equipment as a control means. In such a controlactuator, an instruction side to send instruction to the plant orequipment is insulated from a side performing measurement or driving orcontrolling in the plant side (hereafter referred to as the plant side)depending on use for the purpose of preventing affections of signalvoltage on the human body or evading affections of noise. This isgenerally done by adopting an insulation transformer to transform thevoltage of electric power from the power source or by insulating ainstruction signal sent from the instruction side to plant side from asignal of control result sent from the plant side to the instructionside by means of an insulation transformer, insulation amplifier, etc.

In recent years, there has been an increased demand for performingsoundness diagnosis of circuit in the field of instrumentation andmeasurement for the purpose of raising reliability of the system byconfirming soundness of output signals and circuit wiring, that is, byconfirming whether instruction signals are transmitted accurate to thecontrol means and whether there is a breaking of wire or short circuitoccurred in the circuit.

FIG. 6 and FIG. 7 respectively show an example of conventional drivecircuit of a control actuator and that added with a circuit fordiagnosing soundness of the drive circuit. In the figures, referencenumeral 101 is an electric power source circuit consisting of anelectric power source 102, a pulse generating circuit 103, an insulationtransformer 104, a rectifying circuit 105, and a constant voltagecircuit 106. A broken line 107 indicates an insulation barrier forinsulating the instruction side from the plant side.

First, in a circuit in which soundness diagnosing is not performed asshown in FIG. 6, drive voltage signal 131 of 1.5V, for example, fordriving an actuator 130 is modulated into an alternating signal by amodulating circuit 132, amplified by an insulation transformer 133 whichis a signal insulation means provided to insulate the plant side fromthe instruction side, then demodulated by a demodulating circuit 134supplied with electric power from the electric power source circuit 101,converted by a signal conversion circuit 135 to driving electric powerof for example 25V, 4˜20 mmA, and supplied to a driven object 130 suchas an actuator, the driven object.

However, with the circuit shown in FIG. 6, a signal of what voltage andcurrent is sent to the actuator which is an object to drive can not beknown, and further, although the signal is insulated and sent to theactuator 130, whether the actuator 130 is working normally and whetherthere is a breaking of wire or short circuit in the wiring to theactuator 130, can not be known.

In a circuit added with a circuit to diagnose the soundness thereof asshown in FIG. 7, the driving voltage signal 131 for driving the actuator130 which is the driven object is modulated into an alternating signalby the modulating circuit 132 similarly as in FIG. 6, amplified by theinsulation transformer 133, demodulated by the demodulating circuit 134,converted by the signal conversion circuit 135 into a voltage signal orcurrent signal corresponding to the driving voltage signal 131 to drivethe actuator 130.

In order to confirm the operation of the actuator 130, the drivenobject, there are provided signal conversion circuits 136 a (for currentsignal) and 136 b (for voltage signal) for converting the voltage andcurrent supplied to the actuator 130 from the signal conversion circuit135, which is supplied with electric power from the electric powersource circuit 101, into an alternating signal respectively so as to beable to be inputted to insulation transformers 138 a and 138 brespectively; modulating circuits 137 a and 137 b for modulating theoutputs from the signal conversion circuits 136 a and 136 b; and furtherdemodulating circuit 139 a and 139 b for demodulating the voltagestransformed by the insulation transformers 138 a and 138 b into acurrent signal and voltage signal. With this circuit configuration,whether operation is performed in accordance with the instruction andwhether there is a breaking of wire or short circuit are judgedaccording to whether current is flowing to the actuator 130 and whetherthe applied voltage is a voltage corresponding to actuation of theactuator 130.

As mentioned above, in the conventional circuit, insulation electricpower source circuit 101 including the insulation transformer 104 andconstant voltage circuit 106, and an insulation means such as aninsulation amplifier composed including the insulation transformer 133to insulate signals between the plant side and instruction side, areused in order to drive the actuator 130 (driven object) or to drive thesignal conversion circuit, modulating circuit, and demodulating circuit.Insulated interface of the instruction side and plant side has beenattained in this way. Therefore, in the conventional circuit, aninsulation electric power source circuit and insulation amplifiers areneeded, which results in a large increase in cost.

In the circumstances, the circuit like this has been able to afford tobe applied only in a special case where confirmation of reliability isdemanded in spite of increase in cost, because when performing such asoundness diagnosis that whether voltage signals used in controlling theplant and equipment are transmitted accurately and whether there is abraking of wire or short circuit, additional insulation amplifiers areneeded to carry out give-and-take of signals between the plant side andinstruction side, which requires a large increase of cost.

When performing the soundness diagnosis that whether voltage signalsused in controlling the plant and equipment are transmitted accuratelyand whether there is a braking of wire or short circuit, there occurfollowing problems:

-   -   (A) Transmission of signals and supply of electric power must be        done by separate circuits.    -   (B) A modulation circuit and demodulation circuit are needed in        order to transmit DC signals via an insulation transformer.    -   (C) It is required to convert current signals to voltage signals        because signal transmission is performed by voltage signals.

To suffice item (A), it is needed to provide insulation circuits both tothe electric power source side and signal transmission side, to sufficeitem (B), it is needed to provide modulation circuits and demodulationcircuits to the signal transmission side, and to suffice item (C), it isneeded to provide signal conversion circuits.

As to the art for detect braking of wire, there are disclosed forexample in patent literature 1 (Japanese Laid-Open Patent ApplicationNo. 2006-023105) a method of detecting breaking of wire by applying apulse signal to the wire, and comparing the current wave shape measuredwith the reference current wave shape to judge the presence or absenceof breaking of wire from difference in both the wave shapes, and inpatent literature 2 (Japanese Laid-Open Patent Application No.2004-198302) a circuit for detecting breaking of wire by applying apulse signal for checking via an impedance component to the signal wirefor detecting breaking of wire, and comparing the signal obtained fromthe signal wire with the pulse signal for checking to judge the presenceor absence of breaking of wire.

As to diagnosis of electric circuits, there is disclosed for example inpatent literature 3 (Japanese Laid-Open Patent Application No. 8-005708)a method of diagnosing electric circuits and diagnosing device used forthe method. With which conditions of electric apparatuses are diagnosedfor the purpose of improving efficiency of diagnosis operation byfacilitating measurement record management and further decreasingoccurrence of man-caused errors, by reading out information written andstored in a nonvolatile memory concerning measurement results ofcharacteristics or things concerning measurement of the electricapparatuses, or measurement results of characteristics or thingsconcerning measurement of the electric apparatuses, and comparing theread-out information with the information of-the-moment concerningmeasurement results of characteristics or things concerning measurementof the electric apparatuses.

However, with the art taught in the patent literature 1 and 2, means forapplying pulse signals and a memory for memorizing reference currentwave shape are needed, and with the electric circuit diagnosing devicedisclosed in the patent literature 3, a memory memorized informationconcerning measurement results of characteristics or things concerningmeasurement of the electric apparatuses is needed, and further a meansfor measuring characteristics of the circuit and a means, for comparingthe measurement result with the reference data, resulting in complicatedcomposition. Therefore, problems cited in the items (A)˜(C) can not besolved by these art.

SUMMARY OF THE INVENTION

Therefore, the object of the present invention is to provide a devicefor diagnosing signal status of a driven object, with which a signalshowing the status of a signal given to a control actuator, a drivenobject, or occurrence of a breaking of wire or short circuit, istransmitted by the same means for transmitting the electric power, andtransmission of measurement result and diagnosis of soundness of thecircuit can be performed with high accuracy by simple constructionwithout increase of the number of parts and complication of thecircuitry, thereby preventing increase in manufacturing cost.

To attain the object, the present invention proposes a device fordiagnosing signal status of a driven object, in which a drive voltagesignal for driving the driven object is inputted via an insulationmeans, the driven object is driven by electric drive power correspondingto the inputted voltage, and concurrently signal status of the drivenobject is diagnosed, wherein the device comprising: an insulationtransformer having an intermediate tap at a midpoint of its primarywinding as said insulation means, to the secondary side of which isconnected said driven object, a signal generating means for generatingperiodically vibrating voltage including a rectangular wave pulsevoltage (switching pulse voltage vibrating between 0V and a positivevoltage or a negative voltage) and alternating voltage (voltagevibrating between a positive voltage and a negative voltage) having anamplitude corresponding to that of said inputted drive voltage signalfor driving the driven object connected to the primary side of theinsulation transformer, a current measuring means connected to theintermediate tap of the primary winding of the insulation transformer tomeasure a current generated in the primary side caused by the currentflowing in the driven object connected to the secondary side of theinsulation transformer, a feedback means for converting the currentflowing from the intermediate tap of the primary side to a voltagecorresponding to the drive voltage driving the driven object and feedingback the converted voltage to the input drive voltage signal, and avoltage measuring means for measuring the voltage added with thefeedback voltage, whereby diagnosis of signal state of the driven objectis performed based on measurement results of the current measuring meansand voltage measuring means.

In this way, by measuring the change of the primary side voltage causedby the consumption of the electric power supplied from the primary sideby the driven object connected to the secondary side of the insulationtransformer, converting the measured change of current into a voltagecorresponding to the voltage driving the driven object and feeding backthe converted voltage to the inputted drive voltage, measuring thevoltage added with the feedback voltage, and diagnosing the signalstatus of the driven object based on the measurement results of thecurrent and voltage, transmission of measurement result and diagnosis ofsoundness of the circuit can be performed with high accuracy by simpleconstruction without increase of the number of parts and complication ofthe circuitry, thereby preventing increase in manufacturing cost.

As has been described heretofore, the device for diagnosing signalstatus of a control actuator according to the invention can be composedin very simple construction without increasing the number of parts andcomplicating the circuitry, with a result that increase of manufacturingcost is prevented. In addition, with the device, transmission ofmeasurement result and diagnosis of the soundness of the circuit can beperformed with high accuracy without the need to provide an electricpower source having a constant voltage circuit, insulation means such asan insulation transformer for both the electric power source side andsignal transmitting side, signal conversion circuit, modulating circuit,and demodulating circuit.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of circuit according to the invention fordriving a control actuator such as a servo valve which is fully openedor fully closed upon receiving voltage signal, or a servo valve of whichopening is controlled between fully opened state and fully closed statein accordance with the voltage of a voltage signal.

FIG. 2 is a diagram of a circuitry according to the invention fordriving the control actuator of FIG. 1.

FIG. 3 is a graph showing core loss (electric power loss) vs.temperature characteristic of the core material used in the transformerof the invention.

FIG. 4 is a pattern diagram showing winding of the primary and secondarycoil around the core of the transformer used in the invention.

FIG. 5A is a graph of a test result showing linearity error of transfercharacteristic of the transformer used in the invention (linearity errorfor various core temperature between −40˜85° C. taking the transfercharacterization factor at 25° C. as the reference value), and FIG. 5Bis table showing the specifications of the transformer used in the test.

FIG. 6 is a block diagram of a conventional circuit for driving anactuator such as an electromagnetic valve which is fully opened or fullyclosed upon receiving voltage signal, or a servo valve of which openingis controlled between fully opened state and fully closed state inaccordance with the voltage of a voltage signal.

FIG. 7 is a block diagram of a conventional circuit for driving anactuator such as an electromagnetic valve which is fully opened or fullyclosed upon receiving voltage signal, or a servo valve of which openingis controlled between fully opened state and fully closed state inaccordance with the voltage of a voltage signal.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

A preferred embodiment of the present invention will now be detailedwith reference to the accompanying drawings. It is intended, however,that unless particularly specified, dimensions, materials, relativepositions and so forth of the constituent parts in the embodiments shallbe interpreted as illustrative only not as limitative of the scope ofthe present invention.

FIG. 1 and FIG. 2 is respectively a block diagram and circuitryaccording to the invention applied to a control actuator such as a servovalve of which the opening is controlled between fully opened state andfully closed state in accordance with the voltage of a voltage signal asexplained referring to FIGS. 6 and 7 of a conventional circuit. In FIGS.1 and 2, reference numeral 2 is a pulse generating circuit, 3 is aninsulation transformer, 4 is a rectifying circuit, 6 is a current signalflowing in the primary side of the insulation transformer 3, and abroken line 7 indicates an insulation barrier. Reference numeral 25, 26is respectively a resistance and a condenser for measuring current, 40is a control actuator as a driven object, 41 is a drive voltage signalfor driving the control actuator 40, 42 is an adder, 43 is a currentsignal of measurement result.

Reference numeral 44 is an amplifier which converts the current signal 6as follows:

-   -   (a) when the control actuator is operating normally, converts it        into 0 volt, and    -   (b) when excessively large current flows or breaking of wire        or short-circuit occurs in the circuit, converts the primary        side current 6 corresponding to the secondary side current of        the insulation transformer into a voltage corresponding to the        excessively large current or corresponding to the occurrence of        breaking of wire or short-circuit.

Reference numeral 45 is a voltage signal for diagnosing whether avoltage corresponding to the drive voltage signal 41 is applied to thecontrol actuator 40 or not, 46 is a control microcomputer forcontrolling the adder 42 and amplifier 44 in FIG. 1. Reference numeral47, 48, and 49 is a FET (Field Effect Transistor), 50 is an inductor,and 51 is a diode.

First, referring to the block diagram of FIG. 1, the drive voltagesignal 41 which is a command signal to determine a current to be appliedto the actuator 40, a driven object, is applied to the pulse generatingcircuit 2. The pulse generating circuit 2 generates a pulse of anamplitude corresponding to the drive voltage signal 41. The pulsegenerated by the pulse generating circuit 2 is preferably a rectangularwave but an alternating wave such as a sine curve is also permissible. Avoltage increased in electric pressure corresponding to the drivevoltage signal 41 is outputted from the secondary side of the insulationtransformer 3, the output voltage is rectified by the rectifying circuit4 and sent to the control actuator 40 to drive it. As a currentcorresponding to the electric power consumed by the control actuator 40flows in the primary side of the insulation transformer 3, this currentas the current signal 6 is converted by the amplifier 44 into voltageaccording to the case (a) or (b) as described above, the convertedvoltage is given as feedback to the drive voltage signal 41 via theadder 42, the resultant voltage of the feedback is outputted as theapplying voltage signal 45 of the insulation transformer 3.

That is, in the diagnosing device of signal status of the controlactuator (driven object 40), electric power is consumed as electriccurrent flows in the control actuator 40, a current corresponding tosaid current flows in the primary side of the insulation transformer 3,so this current of the primary side is measured and the current andvoltage flowed or consumed in the control actuator 40 is estimated basedon the measurement result. When there occurs a short circuit, thevoltage signal is measured as a small voltage, and when is a breaking ofwire, the voltage signal is measured as a large voltage, so whetherconnection to the actuator 40 is normal or not can be known, and thesignal status including soundness diagnosis of the connection of theactuator can be recognized.

Next, FIG. 2 which is a concrete circuitry of FIG. 1 which is a blockdiagram will be explained. The actuator 40 is connected to the full-waverectifying circuit 4 connected to the secondary side of the insulationtransformer 3. To the control microcomputer 46 which is provided in theprimary side of the insulation transformer 3 and performs the functionof the adder 42 and amplifier 44 shown in the block diagram of FIG. 1 isinputted the drive voltage signal 41, applied with a voltagecorresponding to the drive voltage signal 41 outputted from the circuitconsisting of the FET 47, diode 51, and inductor 50 supplied with avoltage V_(cc) supplied. The FET 48 and FET 49 for applying, driven bythe pulse generating circuit 2, a voltage from the FET 47 alternately toboth ends of the primary winding of the insulation transformer 3 areprovided.

As an intermediate tap is provided to the primary winding of theinsulation transformer 3, and a voltage is applied to both the ends ofthe primary winding of the insulation transformer 3 alternately by theFET's 48 and 49, a current flows through the circuit consisting of theresistance 25 and condenser 26. This current is sent to the controlmicrocomputer 46 as the current signal 6 to be outputted as the currentsignal 43 and at the same time converted as mentioned before dependingon situations as follows:

-   -   (a) when the control actuator is operating normally, converted        into 0 volt, and    -   (b) when excessively large current flows or breaking of wire        or short-circuit occurs in the circuit, converted into a voltage        corresponding to the excessively large current or corresponding        to the occurrence of breaking of wire or short-circuit. The        converted value is given as feedback to the drive voltage signal        41, and the result is added to the voltage applied to insulation        transformer 3 from the inductor 50 via the FET 48, 49 to obtain        the voltage signal 45.

In the circuit configured like this, a PWM (Pulse Width Modulation)signal is applied to the FET from the microcomputer 46 to which thedrive voltage signal 41 is imputed so that a driving signal of theactuator 40 becomes a signal corresponding to the voltage of the drivevoltage signal 41. For that purpose, a voltage corresponding to thevoltage of the drive voltage signal 41 is applied from the FET 47 to theFET's 48 and 49 to which the pulse is supplied from the pulse generatingcircuit 2. Therefore, a voltage increased in electric pressure tocorrespond to the drive voltage signal 41 is outputted from thesecondary side of the insulation transformer 3 to be sent via therectifying circuit 4 to the control actuator 40 which is not shown inFIG. 2 to drive it.

As a current corresponding to the current flowing to the controlactuator 40 flows in the primary winding of the insulation transformer,the primary side current 6 flowing from the intermediate tap through theresistance and condenser 26 is inputted to the control microcomputer 46,and the primary side current 6 is converted into a voltage depending onthe situations (a) or (b) as described above, and the converted voltageis added via the inductor 50 to the measured voltage to obtain thevoltage signal 45.

To be more specific, when the actuator 40 is operating normally, theprimary side current signal 6 corresponds to the electric power consumedby the control actuator 40, so, by converting the current signal 6 to a0V signal according to the case (a), the voltage signal 45 of the samevoltage value as the voltage signal 41 is outputted. The voltage appliedto the control actuator 40, the driven object, can be estimated byknowing the value of the voltage signal 45 and current signal 6, sowhether the control actuator is working normally or not can be judged.Further, the resistance of the control actuator 40 can be known, so, byconverting the primary side current 6 into a voltage corresponding to amalfunction of the circuit according to the case (b), the voltage of thesignal is measured as a small voltage value when there is a shortcircuit and measured as a large voltage value when there is a breakingof wire. In this way, excess current flow to the control actuator 40,occurrence of braking of wire or short circuit, can be estimated byknowing the value of the current signal 6 and voltage signal 45.

Therefore, a drive circuit can be obtained in which analog signal ofcurrent and voltage applied to the control actuator 40 can betransmitted to the instruction side with high accuracy without providingas shown in FIG. 6 the modulating circuit 132, insulation transformer133 demodulating circuit 134, and signal conversion circuit 135.Further, a circuit provided with a circuit soundness diagnosing devicecan be composed in a simple circuit without providing as shown in FIG. 7the insulation amplifier comprising the signal conversion circuits 136a(for current signal) and 136 b (for voltage signal) for converting thevoltage and current supplied to the actuator 130 from the signalconversion circuit 135 into an alternating signal respectively so as tobe able to be inputted to insulation transformers 138 a and 138 brespectively; modulating circuits 137 a and 137 b for modulating theoutputs from the signal conversion circuits 136 a and 136 b; anddemodulating circuit 139 a and 139 b for demodulating the voltagestransformed by the insulation transformers 138 a and 138 b into acurrent signal and voltage signal; and furthermore inexpensively thanthe conventional circuit without a circuit soundness diagnosing deviceas shown in FIG. 6.

When diagnosing the status of the signal of the control actuator, thedriven object, via the transformer, that is, when estimating the stateof the driven object by measuring the current change generated in theprimary side of the transformer caused by the consumption of electricpower by the operation of the driven object, using an electric powersource not provided with the constant voltage circuit, there arises aproblem of accuracy for the measurement of current flowing to theactuator 40 which is a driven object. Particularly, in the circuitsystem like this, energy loss in the insulation transformer becomes anerror for the transmitted energy. When the error in the signaltransmission is smaller than a required accuracy range, there is noproblem. For example, when error of about 0.2%—0.25% is permissible,conventional transformer can be adopted.

When more precision is required, for example, error must be smaller than0.1%, change of core loss depending on temperature of the transformerbecomes most problematic. However, when the core loss is nearly constantin relation to temperature, it is no matter to judge the measurementresult with high accuracy taking temperature into consideration, andmeasurement and transfer of analog signals is made possible with highaccuracy.

FIG. 3 is a graph showing core loss characteristic (loss power (kW/cm³)vs. temperature (° C.)) of several core materials. Core materials PC44and PC47 of TDK Ltd. made which has a peak value at near 100° C.,however, PC95 also of TDK Ltd. made has a relatively flat core losscharacteristic. In the invention, PC95 was adopted as the core materialof the insulation transformer. By this, a signal status diagnosingdevice can be provided which performs diagnosis of the status of signalsin the measurement and control means in the driven object with highaccuracy.

Further, the inventors of the application composed a transformer suchthat an intermediate tap is provided in an intermediate part of theprimary winding, a current measuring means is connected to theintermediate tap, and change of primary side current caused byconsumption of current supplied to the secondary side. As shown in FIG.4, the primary coil is divided into an anterior half 11 and posteriorhalf 13 such that a secondary coil 12 is sandwiched by both the primarycoil 11 and 13, and the intermediate tap is taken out from the center ofthe primary coil. The inventors found out that a favorable signaltransfer characteristic can be obtained with this composition of atransformer using PC95 as core material.

FIG. 5A is a graph showing a test result. The test was performedcomposing a distributor-isolation-amplifier using a insulationtransformer composed using PC95 of TDK made as core material andarranging primary and secondary windings as shown in FIG. 4. Linearityand temperature drift were measured.

Specification of the insulation transformer used in the test is shown inthe table of FIG. 5B. Measurement was performed using a precisionresistance of accuracy of 10 ppm/° C.

In FIG. 5A is shown linearity errors of transfer characteristics fortemperatures between −40-85° C., in which output currents (mA) of thedistributor-isolation-amplifier are plotted as the abscissa and fullscale errors % (4˜20 mA is taken as 100%) are plotted as the ordinate,with the transfer characteristic factor at 25° C. taken as the referencevalue.

In the case of the conventional transformer composed by using PC44 orPC47 as core material to have a single primary coil not divided in twoas shown in FIG. 4 and a secondary coil wound over the primary coil,linearity is 10.05% or smaller, and about ±0.25% under environment of0˜60° C. Therefore, as can be recognized from FIG. 5A that, by composingthe insulation transformer as described before, linearity of ±0.01% orsmaller, about ±0.1% under environment of 0˜85° C., and about0.15%˜−0.1% under environment of −40˜85° C. can be attained. It isthinkable that further improvement in accuracy and temperaturecharacteristic can be attained by innovations in shape and size andincrease of the number of winding of the insulation transformer. Byadopting the insulation transformer like this, diagnosing of the signalstatus of the actuator can be performed with high accuracy by simplecircuitry.

INDUSTRIAL APPLICABILITY

According to the invention, provision of means for diagnosing signalstatus of a control actuator, which has been hesitated in the pastbecause of increase in manufacturing cost, can be implemented withsimple construction and without increase in the number of constituentelements, complication of the circuit configuration, and increase inmanufacturing cost. The invention can be applied easily to an electriccircuit which is required particularly to be highly reliable.

1. A device for diagnosing signal status of a driven object, in which adrive voltage signal for driving the driven object is inputted via aninsulation means, the driven object is driven by electric drive powercorresponding to the inputted voltage, and concurrently signal status ofthe driven object is diagnosed, wherein the device comprising: aninsulation transformer having an intermediate tap at a midpoint of itsprimary winding as said insulation means, to the secondary side of whichis connected said driven object, a signal generating means forgenerating periodically vibrating voltage including a rectangular wavepulse voltage and alternating voltage having an amplitude correspondingto that of said inputted drive voltage signal for driving the drivenobject connected to the primary side of the insulation transformer, acurrent measuring means connected to the intermediate tap of the primarywinding of the insulation transformer to measure a current generated inthe primary side caused by the current flowing in the driven objectconnected to the secondary side of the insulation transformer, afeedback means for converting the current flowing from the intermediatetap of the primary side to a voltage corresponding to the drive voltagedriving the driven object and feeding back the converted voltage to theinput drive voltage signal, and a voltage measuring means for measuringthe voltage added with the feedback voltage, whereby diagnosis of signalstate of the driven object is performed based on measurement results ofthe current measuring means and voltage measuring means.